Antagonistic actions of boron against inhibitory effects of aluminum toxicity on growth, CO₂assimilation, ribulose-1,5-bisphosphate carboxylase/oxygenase, and photosynthetic electron transport probed by the JIP-test, of <it>Citrus grandis </it>seedlings

• Main Authors: Tang Ning, Jiang Huan-Xin, Zheng Jin-Gui, Chen Li-Song
• Format: Article
• Language: English
• Published: BMC 2009-08-01
• Series: BMC Plant Biology
• Online Access: http://www.biomedcentral.com/1471-2229/9/102

<p>Abstract</p> <p>Background</p> <p>Little information is available on the amelioration of boron (B) on aluminum (Al)-induced photosynthesis inhibition. Sour pummelo (<it>Citrus grandis</it>) seedlings were irrigated for 18 weeks with nutrient solution containing 4 B levels (2.5, 10, 25 and 50 μM H₃BO₃) × 2 Al levels (0 and 1.2 mM AlCl₃·6H₂O). The objectives of this study were to determine how B alleviates Al-induced growth inhibition and to test the hypothesis that Al-induced photosynthesis inhibition can be alleviated by B <it>via </it>preventing Al from getting into shoots.</p> <p>Results</p> <p>B had little effect on plant growth, root, stem and leaf Al, leaf chlorophyll (Chl), CO₂assimilation, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), Chl a fluorescence (OJIP) transient and related parameters without Al stress except that root, stem and leaf B increased with increasing B supply and that 50 μM B decreased slightly root dry weight. Al-treated roots, stems and leaves displayed a higher or similar B. B did not affect root Al under Al stress, but decreased stem and leaf Al level. Shoot growth is more sensitive to Al stress than root growth, CO₂assimilation, Chl, Rubisco, OJIP transient and most related parameters. Al-treated leaves showed decreased CO₂assimilation, but increased or similar intercellular CO₂concentration. Both initial and total Rubisco activity in Al-treated leaves decreased to a lesser extent than CO₂assimilation. Al decreased maximum quantum yield of primary photochemistry and total performance index, but increased minimum fluorescence, K-band, relative variable fluorescence at J- and I-steps. B could alleviate Al-induced increase or decrease for all these parameters. Generally speaking, the order of B effectiveness was 25 μM > 10 μM ≥ 50 μM (excess B) > 2.5 μM.</p> <p>Conclusion</p> <p>We propose that Al-induced photosynthesis inhibition was mainly caused by impaired photosynthetic electron transport chain, which may be associated with growth inhibition. B-induced amelioration of root inhibition was probably caused by B-induced changes in Al speciation and/or sub-cellular compartmentation. However, B-induced amelioration of shoot and photosynthesis inhibition and photoinhibitory damage occurring at both donor and acceptor sides of photosystem II could be due to less Al accumulation in shoots.</p>